tire increase to correct speedo

[slyhog-22056]

Recently I changed the tranny in my BMW, now the speed in off by 7 mph, and I have to run approx 300 rpm more to keet the same speed I used too. my speedo is driven by the rear end pinion I need to know how much bigger the tires need to be to correct 7 mph. My current tires are 14" with a diameter of 24".

[drdisque]

its off by 7mph at what speed? off 300 rpm at what speed? We need a percentage change to help you, not a numerical change at an unknown speed.

[slyhog-22056]

Originally Posted by drdisque

its off by 7mph at what speed? off 300 rpm at what speed? We need a percentage change to help you, not a numerical change at an unknown speed.

At 3000 rpm in 5th gear I now am doing 70 mph, It used to be about 2650 rpm @ 70 mph, it appears to be off by 10% all the way through. I have 14" factory tires with a diameter of 24". My concern isnt about highway speeds, in 1st and second it is very easy to break the rear end loose and smoke the tires, BTW I AM a very agressive driver and 1st only gets me to 35 mph now (5000 rpm) and second to 45. Driving around Dallas in 3rd gear @ 2500 rpm just to go 40 is a pain in the ZZZ
I have found some old chevrolet wheels (15 x 8) with 4.75" hole spacing with adapters for the center hole to fit BMW. The BMW is 4.73" hole diameter, will the .02" make a difference with the centering spacer?? The wheels were on a 1986 735
Sorry I didnt give better information the first time around

[drdisque]

I personally wouldn't swap over to those wheels, just because you'd have to use adapters. If you give us your current tire size we can probably find one that will run about 11.6% bigger

[slyhog-22056]

My current tire size is 260-50 R 14. And I want to go at least 2" wider on tire track width. I wouldnt have to use adapterswith the Chev wheels, BMW sells the rings to match different center holes on different, or is the .02" too much difference in bolt diameter??? I dont have very deep pockets so I was trying to keep the costs down. I dont know of another make car with the same 120 mm bolt wheels.

[drdisque]

are you sure thats your size? because all first numbers end in 5.

if your size is 265/50-14 it does look like it would be easier to go up to 15's with 255/60-15's which would be about 11% bigger than your existing tires.

I know of people that have used that GM bolt pattern with BMW's without problems